The present invention relates to a device intended for cutting laminar elements to their proper length. The invention has been developed with particular attention paid to its possible use in the field of plants for the fabrication of such hygienic and sanitary products as sanitary towels, nappies, baby diapers, etc.
On the basis of one of the solutions that is very widely used today, these products are fabricated in continuous or "in line" processes, that is to say, starting from a plurality of strips or webs that are superposed and paired in various ways to obtain a final strip or web from which the individual final products can then be obtained (generally by means of a cutting operation).
In the course of the various phases of the aforesaid fabrication process--and even in the phases that follow the obtainment of the individual final products--there may arise the need for applying to a moving element (quite irrespective of whether this element is of the continuous type or forms part of a continuous or substantially continuous flow of distinct elements) some laminar elements that, with a view to that application, have to be cut to length. As a general rule, the cutting operation is realized in a phased manner, because it is intended to generate elements capable of being applied at a predetermined rhythm (and, more often than not, in keeping with a given "phasing") related to the output flow rate.
The satisfaction of these needs is rendered more critical by the fact that most of the time the laminar elements in question have to have a length that is different from the length of the articles to which they have to be applied (as a general rule, they have to be "shorter").
For example, the laminar element that has to be cut to length may be the absorbing core or pad of a hygienic or sanitary product that has an overall length greater than that of the absorption pad it contains: to render the idea a little clearer, one needs only think of the distance that separates the two waist lines of a normal pair of nappies or diapers, a distance that is usually greater than that of the anteroposterior length of the absorption pad. Another example of a laminar element that may have to be cut to length before being applied in a rhythmic manner to a flow of articles is constituted by the label or labels (which are generally made of siliconized paper) that have to be applied to the zones of a hygienic or sanitary article treated with adhesive material. As a typical example, the present description will henceforth make reference to ladies' sanitary towels of the type generally known as "winged". In this case the finished product has three zones that have been treated with adhesives: one of these extends along the principal median axis of the towel and permits it to be accurately positioned in the crotch portion of the slip of the wearer, while the other two, which are of shorter length, are situated on the wings to permit the bent-back wings to adhere to a position below the crotch portion of the slip. In all three cases the adhesive-protection label has a length shorter than the overall length of the product (and, in the case of the labels to be applied to the wings, also much shorter). There is thus need for arranging things in such a way that the labels can be i) cut to the desired length and ii) accurately applied in the position of the adhesive zone that the label is to protect.
The machines used at present to satisfy these needs are based on a configuration that can be defined as a transfer; after being fed to the machine in the form of a strip, the material of which the labels are made is first subjected to a cutting operation by means of a head provided with revolving knives acting on a receiving counter-roller that subsequently also undertakes the actual application of the labels to the articles as they move forward.
When a given production line is expected to be used for the realization of either different products or the same product in different formats, so that there is need to have available elements cut into different lengths, it becomes necessary to use cutting and/or application devices of different types that have to be appropriately substituted for each other in order to obtain products having the desired characteristics. All this becomes translated into a greater global cost of the plant and, above all, the need of shutting down the plant, sometimes for rather long periods of time, whenever one has to pass to the production of an article having characteristics different from the article of the previous production run (the so-called "format changes").